Past Papers PPSC Electrical Engineering

1. : What is the purpose of using a breather in a transformer? (NTDC Electrical Engineer – 2022)

(A) To remove moisture from the air entering the conservator tank

(B) To increase cooling efficiency

(C) To filter transformer oil

(D) To detect internal faults

2. : Which part of the transformer is laminated to reduce eddy current losses? (PPSC Assistant Engineer Electrical – 2021)

(A) Windings

(B) Core

(C) Tank

(D) Bushings

3. : The primary function of a transformer is to? (WAPDA Electrical Engineer – 2020)

(A) Convert AC to DC

(B) Step up or step down voltage

(C) Store electrical energy

(D) Measure current

4. : In a transformer, the no-load current is approximately what percentage of the full-load current? (NTDC Electrical Engineer – 2023)

(A) 1–2%

(B) 5–10%

(C) 20–25%

(D) 30–35%

5. : Which test is conducted on a transformer to determine copper losses? (PPSC Electrical Engineer – 2021)

(A) Open-circuit test

(B) Short-circuit test

(C) Insulation test

(D) Polarity test

6. : Which type of cooling is used in large power transformers? (LESCO Engineer Recruitment Test – 2022)

(A) Air natural

(B) Oil natural air natural (ONAN)

(C) Air blast

(D) Water cooling

7. : What is the function of a tap changer in a transformer? (PESCO Electrical Engineer – 2021)

(A) To change the turns ratio for voltage regulation

(B) To increase efficiency

(C) To change frequency

(D) To control temperature

8. : The instrument used to measure insulation resistance is? (WAPDA Electrical Engineer – 2019)

(A) Wattmeter

(B) Voltmeter

(C) Megger

(D) Multimeter

9. : Which of the following is NOT a type of transformer loss? (NTDC Electrical Engineer – 2023)

(A) Core loss

(B) Copper loss

(C) Friction loss

(D) Eddy current loss

10. : The efficiency of a transformer is maximum when? (PPSC Electrical Engineer – 2020)

(A) Iron losses = Copper losses

(B) Iron losses < Copper losses

Copper losses” onclick=”checkAnswer(‘q10’, ‘Iron losses = Copper losses’)”> (C) Iron losses > Copper losses

(D) Iron losses are zero

11. : The main reason for transformer humming noise is? (NTDC Electrical Engineer – 2023)

(A) Vibration of windings due to magnetostriction in the core

(B) Loose joints in the tank

(C) Oil circulation

(D) Air bubbles in winding insulation

12. : What is the typical value of transformer oil temperature rise over ambient temperature? (PPSC Electrical Engineer – 2021)

(A) 10–20°C

(B) 30–40°C

(C) 45–55°C

(D) 60–70°C

13. : In a power transformer, the leakage flux is minimized by? (WAPDA Electrical Engineer – 2020)

(A) Using laminated core

(B) Using concentric windings

(C) Increasing air gap

(D) Using higher resistance conductors

14. : What is the purpose of a conservator tank in an oil-filled transformer? (LESCO Engineer Recruitment Test – 2021)

(A) To provide space for oil expansion and contraction

(B) To store excess oil permanently

(C) To cool the transformer core

(D) To collect impurities

15. : What is the approximate efficiency of a large power transformer at full load? (PESCO Electrical Engineer – 2020)

(A) 50%

(B) 70%

(C) 90%

(D) 98%

16. : Which device is used to measure the oil level in a transformer conservator? (NTDC Electrical Engineer – 2022)

(A) Thermometer

(B) Hydrometer

(C) Magnetic oil gauge

(D) Pressure gauge

17. : The insulation resistance of a transformer should be tested with? (PPSC Assistant Engineer Electrical – 2021)

(A) Multimeter

(B) Megger

(C) Earth tester

(D) Ohmmeter

18. : The main cause of transformer efficiency reduction is? (WAPDA Electrical Engineer – 2021)

(A) Core losses

(B) Copper losses

(C) Leakage reactance

(D) Both (A) and (B)

19. : What type of transformer is used for electrical isolation without voltage change? (NTDC Electrical Engineer – 2023)

(A) Step-up transformer

(B) Step-down transformer

(C) Isolation transformer

(D) Auto-transformer

20. : The main advantage of an auto-transformer over a two-winding transformer is? (PPSC Electrical Engineer – 2021)

(A) Higher losses

(B) Larger size

(C) Higher efficiency and smaller size

(D) Lower voltage regulation

21. : The frequency of an alternator depends on? (PPSC Electrical Engineer – 2021)

(A) Speed of rotor only

(B) Number of poles only

(C) Both speed and number of poles

(D) Type of stator winding

22. : In an alternator, the generated EMF is directly proportional to? (WAPDA Electrical Engineer – 2020)

(A) Speed

(B) Flux per pole

(C) Number of turns

(D) All of the above

23. : The rotating part of an alternator is known as? (NTDC Electrical Engineer – 2022)

(A) Stator

(B) Rotor

(C) Armature

(D) Commutator

24. : What happens if the field current of a synchronous motor is increased beyond the normal value? (PESCO Electrical Engineer – 2021)

(A) Power factor decreases

(B) Power factor becomes lagging

(C) Power factor becomes leading

(D) Motor speed increases

25. : The armature winding of an alternator is usually placed on? (LESCO Assistant Engineer – 2022)

(A) Rotor

(B) Stator

(C) Shaft

(D) Slip rings

26. : The main purpose of damper windings in a synchronous motor is to? (NTDC Electrical Engineer – 2023)

(A) Reduce noise

(B) Prevent hunting

(C) Increase efficiency

(D) Reduce armature reaction

27. : The emf generated per phase in an alternator is given by? (PPSC Sub Engineer Electrical – 2020)

(A) 2.22 f N Φ

(B) 4.44 f N Φ

(C) 2 f N Φ

(D) 1.11 f N Φ

28. : When a synchronous motor runs at no load and unity power factor, its armature current is? (WAPDA Electrical Engineer – 2021)

(A) Minimum

(B) Maximum

(C) Zero

(D) Constant

29. : The voltage regulation of an alternator is negative when the load power factor is? (LESCO Electrical Engineer – 2020)

(A) Lagging

(B) Unity

(C) Leading

(D) Zero

30. : Which method is commonly used to determine voltage regulation of an alternator? (PPSC Electrical Engineer – 2022)

(A) Short-circuit test

(B) Open-circuit test

(C) Synchronous impedance method

(D) Slip test

31. : In a three-phase induction motor, the rotating magnetic field rotates at? (PPSC Electrical Engineer – 2021)

(A) Synchronous speed

(B) Rotor speed

(C) Slip speed

(D) Half synchronous speed

32. : The starting torque of a squirrel cage induction motor is generally? (WAPDA Electrical Engineer – 2020)

(A) Low

(B) High

(C) Infinite

(D) Same as full-load torque

33. : The slip at full load in an induction motor is typically about? (LESCO Sub Engineer Electrical – 2021)

(A) 0.1%

(B) 1%–3%

(C) 5%–8%

(D) 10%–15%

34. : Which method is used to control the speed of an induction motor above its synchronous speed? (PESCO Electrical Engineer – 2022)

(A) Rotor resistance control

(B) Stator voltage control

(C) Cascade connection

(D) None, it cannot be operated above synchronous speed

35. : In a 3-phase induction motor, the torque is maximum when? (PPSC Electrical Engineer – 2021)

(A) Rotor resistance equals rotor reactance

(B) Rotor reactance is zero

(C) Slip is zero

(D) Supply frequency is maximum

36. : The starting torque of a DC series motor is? (WAPDA Electrical Engineer – 2020)

(A) Low

(B) Medium

(C) High

(D) Zero

37. : The direction of rotation of a DC motor can be reversed by? (NTDC Electrical Engineer – 2023)

(A) Reversing field connections only

(B) Reversing armature connections only

(C) Reversing either field or armature connections

(D) Reversing both field and armature connections simultaneously

38. : In a DC generator, the function of the commutator is to? (PPSC Sub Engineer Electrical – 2020)

(A) Convert AC to DC

(B) Convert DC to AC

(C) Reduce losses

(D) Increase efficiency

39. : The speed of a DC shunt motor is almost constant because? (LESCO Electrical Engineer – 2021)

(A) Flux is proportional to armature current

(B) Flux remains practically constant

(C) Armature resistance is very high

(D) Field current varies with load

40. : The back EMF in a DC motor is proportional to? (WAPDA Electrical Engineer – 2022)

(A) Armature current

(B) Field current

(C) Speed and flux

(D) Load torque

41. : The primary source of energy in a thermal power plant is? (PPSC Electrical Engineer – 2021)

(A) Coal

(B) Diesel

(C) Natural Gas

(D) All of these

42. : The efficiency of a thermal power plant is usually in the range of? (WAPDA Electrical Engineer – 2020)

(A) 15–25%

(B) 25–35%

(C) 35–45%

(D) 45–60%

43. : In a hydroelectric power plant, the energy of water is converted into? (PPSC Assistant Engineer Electrical – 2022)

(A) Mechanical energy by turbine

(B) Heat energy

(C) Chemical energy

(D) Electrical energy directly

44. : The capacity of a generator in a power station is usually expressed in? (NTDC Electrical Engineer – 2023)

(A) kW

(B) MW

(C) MVA

(D) kVA

45. : The ideal power factor for maximum efficiency in power transmission is? (LESCO Electrical Engineer – 2021)

(A) 0.5

(B) 0.707

(C) 1.0

(D) 0.9

46. : The load factor of a power plant is defined as? (WAPDA Electrical Engineer – 2022)

(A) Ratio of average load to maximum demand

(B) Ratio of maximum demand to average load

(C) Ratio of plant capacity to load factor

(D) Ratio of connected load to maximum demand

47. : Which generator is used in a hydroelectric power station? (PPSC Electrical Engineer – 2020)

(A) DC generator

(B) Synchronous generator

(C) Induction generator

(D) Variable frequency generator

48. : The transmission efficiency increases when? (NTDC Electrical Engineer – 2023)

(A) Line voltage is increased

(B) Line current is increased

(C) Power factor is reduced

(D) Line losses are increased

49. : In power systems, corona loss increases with? (LESCO Electrical Engineer – 2022)

(A) Decrease in voltage

(B) Increase in frequency

(C) Decrease in conductor size

(D) Increase in conductor spacing

50. : The sag in an overhead transmission line increases when? (PESCO Electrical Engineer – 2021)

(A) Tension is increased

(B) Temperature increases

(C) Weight of conductor decreases

(D) Span is reduced

51. : The main function of protective relays in a power system is to? (PPSC Electrical Engineer – 2021)

(A) Protect equipment from overloading

(B) Detect faults and isolate faulty sections

(C) Control system voltage

(D) Maintain frequency

52. : A Buchholz relay is used for the protection of? (WAPDA Electrical Engineer – 2020)

(A) Transmission line

(B) Transformer

(C) Alternator

(D) Induction motor

53. : An overcurrent relay operates when? (NTDC Electrical Engineer – 2022)

(A) The current exceeds a preset value

(B) Voltage falls below rated value

(C) Frequency increases

(D) Power factor decreases

54. : Differential protection is based on the principle of? (LESCO Electrical Engineer – 2021)

(A) Comparing currents at two ends of equipment

(B) Comparing voltages across a line

(C) Measuring reactive power

(D) Detecting frequency change

55. : A lightning arrester is connected between? (PESCO Electrical Engineer – 2022)

(A) Phase and neutral

(B) Phase and ground

(C) Phase and phase

(D) Neutral and earth

56. : The primary purpose of a circuit breaker is to? (PPSC Assistant Engineer Electrical – 2020)

(A) Control reactive power

(B) Interrupt short-circuit currents

(C) Step down voltage

(D) Measure current

57. : Which of the following circuit breakers uses compressed air for arc extinction? (NTDC Electrical Engineer – 2023)

(A) Air-blast circuit breaker

(B) Vacuum circuit breaker

(C) Oil circuit breaker

(D) SF₆ circuit breaker

58. : The arc in a circuit breaker is extinguished by? (WAPDA Electrical Engineer – 2021)

(A) Cooling and lengthening of arc

(B) Increasing resistance of arc path

(C) Separation of contacts

(D) All of these

59. : SF₆ circuit breakers are preferred for high voltage applications because SF₆ gas has? (LESCO Electrical Engineer – 2022)

(A) High thermal conductivity

(B) Excellent dielectric strength

(C) Arc-quenching properties

(D) All of these

60. : In a power system, the relay operates but circuit breaker fails to trip — this condition is known as? (PPSC Electrical Engineer – 2021)

(A) Back feeding

(B) Breaker failure

(C) Overreach

(D) Underreach

61. : In a DC shunt motor, if the field winding is opened while the motor is running, the motor will: (NTDC Electrical Engineer – 2023)

(A) Stop immediately

(B) Run at dangerously high speed

(C) Run at reduced speed

(D) Burn due to short circuit

62. : The open-circuit test on a transformer primarily measures: (PESCO Electrical Engineer – 2022)

(A) Copper losses

(B) Iron losses

(C) Efficiency

(D) Regulation

63. : The short-circuit test on a transformer is conducted to determine: (WAPDA Electrical Engineer – 2021)

(A) Iron losses

(B) Efficiency

(C) Copper losses

(D) Voltage regulation

64. : The core of a transformer is laminated to reduce: (NTDC Electrical Engineer – 2023)

(A) Hysteresis losses

(B) Eddy current losses

(C) Copper losses

(D) Magnetic flux

65. : The voltage regulation of a transformer is maximum at: (FESCO Electrical Engineer – 2022)

(A) Unity power factor

(B) Lagging power factor

(C) Leading power factor

(D) Zero power factor

66. : The primary and secondary windings of a transformer are: (NTDC Electrical Engineer – 2021)

(A) Conductively coupled

(B) Magnetically coupled

(C) Inductively isolated

(D) Electrically connected

67. : The efficiency of a transformer is maximum when: (PESCO Electrical Engineer – 2023)

(A) Copper losses are minimum

(B) Iron losses are minimum

(C) Copper losses = Iron losses

(D) Load is full

68. : Which of the following motors is best suited for constant speed applications? (LESCO Electrical Engineer – 2022)

(A) DC shunt motor

(B) DC series motor

(C) Universal motor

(D) Stepper motor

69. : The speed of a DC shunt motor can be controlled by varying: (NTDC Electrical Engineer – 2023)

(A) Supply voltage

(B) Armature resistance

(C) Field current

(D) Any of the above

70. : The back emf in a DC motor is directly proportional to: (PESCO Electrical Engineer – 2022)

(A) Armature current

(B) Speed of the motor

(C) Supply voltage

(D) Torque

71. : In a DC generator, the purpose of the commutator is to: (PPSC Electrical Engineer – 2021)

(A) Convert AC to DC

(B) Convert DC to AC

(C) Reduce armature reaction

(D) Provide mechanical support

72. : In a DC motor, torque is directly proportional to: (WAPDA Electrical Engineer – 2020)

(A) Armature voltage only

(B) Flux and armature current

(C) Speed and flux

(D) Resistance and current

73. : What is the function of a starter in a DC motor? (LESCO Electrical Engineer – 2021)

(A) To increase speed

(B) To limit starting current

(C) To reduce torque

(D) To control temperature

74. : The main cause of sparking at brushes in a DC machine is: (PESCO Electrical Engineer – 2022)

(A) High armature current

(B) Poor commutation

(C) High speed

(D) Field weakening

75. : The armature reaction in a DC generator causes: (PPSC Sub Engineer Electrical – 2022)

(A) Increase in terminal voltage

(B) Distortion of main flux

(C) Increase in armature resistance

(D) Decrease in speed

76. : The efficiency of a DC generator is maximum when: (WAPDA Electrical Engineer – 2019)

(A) Iron losses = Copper losses

(B) Load current is maximum

(C) Copper losses = Stray losses

(D) Mechanical losses = Electrical losses

77. : In a DC motor, back EMF is produced because of: (NTDC Electrical Engineer – 2023)

(A) Lenz’s Law

(B) Faraday’s Law of Electromagnetic Induction

(C) Fleming’s Left-Hand Rule

(D) Joule’s Law

78. : The speed of a DC shunt motor can be controlled by varying: (PPSC Assistant Engineer Electrical – 2021)

(A) Supply voltage

(B) Field current

(C) Load torque

(D) Armature resistance only

79. : In a DC series motor, the speed is inversely proportional to: (WAPDA Sub Engineer Electrical – 2020)

(A) Armature voltage

(B) Armature current

(C) Field flux

(D) Supply voltage

80. : The function of interpoles in a DC machine is to: (PESCO Electrical Engineer – 2022)

(A) Reduce armature reaction

(B) Improve commutation

(C) Increase speed

(D) Reduce losses